package com.shr.netease;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class Main2 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in) ;
		int count  = sc.nextInt();
		List<Integer> list = new ArrayList<>();
		for(int i = 0;i<count;i++){
			list.add(sc.nextInt()) ;
		}
		sc.close();
		
		Collections.sort(list);
		
		int diff = list.get(1) - list.get(0) ;
		for(int i = 2;i<list.size();i++){
			if(list.get(i) - list.get(i-1) != diff){
				System.out.println("Impossible");
				return ;
			}
		}
		System.out.println("Possible");
	}
}
